Recently, endoscopes have found wide use in medical fields and in industry. More recently, the pain that is normally associated with the use of an endoscope has been eliminated for some endoscope applications by the development of a capsule endoscope. Japanese Laid-Open Patent Application 2001-91860 is one example of such an endoscope, wherein an objective optical system, image pickup, and light source are contained within a capsule that is swallowed by a patient. The light source employs light emitting elements that are symmetrically arranged within a nearly semi-spherical transparent cover, and objects that are positioned within an observation range illuminated by the light emitting elements are imaged by the objective optical system onto the image pickup.
In the above-mentioned patent publication, an objective lens system and two illuminators are fixed inside the nearly semi-spherical transparent cover, and a lens barrel which supports the objective lens system is moved for focus adjustment and then is fixed in position with a fixing screw. When multiple light emitting elements are arranged at the periphery of an objective optical system, as in the above-mentioned patent publication, observation and diagnosis are made difficult if there exists any offset or change in the illumination onto an irradiated surface. Moreover, in a coelomic observation, sometimes inner wall parts of lumens, such as the esophagus and the intestinal canal, etc., are the objects of interest for observation, in which case the periphery of the field of view of the objective optical system must be brightly illuminated rather than near the center of the field of view. On the other hand, sometimes a gastric wall, or some other object in a relatively large space such as the stomach, is taken as the object of observation wherein it is desirable to brightly illuminate an area near the center of the field of view.
Furthermore, dust or particles such as shaving dregs created when a lens frame is moved when performing an initial focus adjustment of the objective optical system can easily settle on the image surface of the image pickup, causing the likelihood to be too high that images detected by the image pickup will be degraded.